This invention relates to tape cartridges of the belt driven type.
One type of tape cartridge includes a tape whose ends form a supply roll of tape and a takeup roll of tape, and which is driven by a drive belt that bears against the two rolls of tape to turn them. The drive belt can extend around a driven roller and around a pair of corner guide rollers that hold the belt in a path wherein it presses against the tape rolls. It is known that drag applied to the drive belt produces a differential in belt tension which produces tension in the tape. Tape tension is produced, because tension in that portion of the belt that presses on the takeup toll, causes elongation of the belt and therefore causes the belt to move slightly faster so that it tends to drive the takeup roll slightly faster and create tension in the tape. The most common method of producing such belt drag, is to apply friction to the belt or to a guide roller about which the belt extends. For example, U.S. Pat. No. 3,692,255 by Von Behren describes a tape cartridge wherein drag on the belt is achieved by friction between the guide rollers and the shafts on which they rotate.
The use of friction to produce drag on the drive belt, such as by friction between a belt guide roller and the shaft on which it rotates, can result in large variations in belt drag and therefore in tape tension. This is because such friction is very difficult to control so as to remain close to a predetermined level. For example, the precise level of friction between a rotating roller and its shaft can be affected by microscopic particles lying on the shaft, the precise finish of the inside of the roller and of the shaft, and other factors that are extremely difficult to control. Oil on the shaft can help reduce variation in friction, but the variations are still large. The drag on the belt also can be controlled by connecting a miniature electric generator to the guide rollers to retard them, but this adds considerably to the cost of the cartridge. A tape cartridge of simple design which enabled relatively close control of drive belt drag would enable the production of tape cartridges having more closely controlled characteristics, which is especially useful for data recording but is also useful in voice and music applications.